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9600 power supply failure modes/schematic?

Franklinstein

Well-known member
A while back I got a 9600/233, and it mostly worked pretty well (honestly I only bought it because it was $10 and had a G3 upgrade in it). However one day I plugged it in and *pop*. Power supply's out. Inrush probably killed something.

I checked it and the fuse is fine, nothing is on fire or visibly damaged, primary power (roughly 300VDC) is going through from the power input board to the other board, but there's no 5VSB voltage being generated so it can't turn on. I think a power transistor or diode died in the standby/soft power circuit but in situ my DMM doesn't show anything as obviously faulty, just that power stops at some point on the power input board. Is anybody familiar with these or have a schematic available? I didn't see anything suitable in search, either here or on the internet at large.
 

Franklinstein

Well-known member
A little sleuthing later and I found a couple open components in the 5vsb circuit. Sadly I couldn't find usable information for testing some of the VRMs (they require specific bench-testing configurations with power supplies and things, a DMM probe won't really tell you anything other than pure open/short) so I replaced a resistor or two, but it still doesn't work. Not finding any obvious problems, I applied power but one of the new resistors exploded, though the fuse didn't blow. Seems something's drawing way too much power through that circuit on the primary side of the always-on/trickle transformer. The transformer is between 6-30 ohms on basically any set of pins on primary or secondary but I don't know if that's good or not since I can't find any info for it. Either way nothing immediately flags as shorted, and that has to be the problem. Maybe one of the VRMs is bad but again they appear to give unsurprising values when checked out-of-circuit with a DMM, certainly no dead shorts, but I can't know if they actually work right since I lack the bench testing equipment for them. I may end up just trying to do an ATX swap on this thing.
 
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